The problem asks us to find the expression for $(f-g)(x)$ given $f(x) = x^2 - 1$ and $g(x) = x^2 + x$.

1. Problem Description

The problem asks us to find the expression for $(f-g)(x)$ given $f(x) = x^2 - 1$ and $g(x) = x^2 + x$.

2. Solution Steps

We need to find $(f-g)(x)$, which is defined as $f(x) - g(x)$.

$f(x) = x^2 - 1$

$g(x) = x^2 + x$

$(f-g)(x) = f(x) - g(x) = (x^2 - 1) - (x^2 + x)$

$(f-g)(x) = x^2 - 1 - x^2 - x$

$(f-g)(x) = x^2 - x^2 - x - 1$

$(f-g)(x) = -x - 1$

$(f-g)(x) = -1 - x$

3. Final Answer

The final answer is (C) $-1 - x$.